[jdk11u-dev] RFR: 8305733: Pattern.CASE_INSENSITIVE does not take effect in jdk11

[Korov]

fix [JDK-8305733](https://bugs.openjdk.org/browse/JDK-8305733)

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Commit messages:
 - add jtreg test
 - fix Pattern.CASE_INSENSITIVE not work

Changes: https://git.openjdk.org/jdk11u-dev/pull/2062/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2062&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305733
  Stats: 131 lines in 3 files changed: 90 ins; 0 del; 41 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2062.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2062/head:pull/2062

PR: https://git.openjdk.org/jdk11u-dev/pull/2062